High voltage cables or conductors for installation in cable ducts or on the sea bed are normally coated with a plastics material by an extrusion process.
In such a process it is a desired requirement that the cable dimesion and position in the extrusion run be monitored constantly in order that the final product conforms to manufacturers specifications. In some instances a special semi-conductor insulant is applied in the extrusion process known in the art as a vulcanizing process, in which the insulation has to be applied under pressure by means of steam or nitrogen gas, at an elevated temperature.
Due to this and the hostile environment in which curing of the coating takes place a non-contact dimensional measurement technique is required.
Present known techniques are plagued with problems, in particular the difficulty of obtaining accurate measurements in the absence of direct contact due to the presence of contamination between the object being measured and the remote measuring instrumentation.